Increasing security risks have led to a demand for telephone calls to be monitored. One form of monitoring is the lawful interception by a law enforcement agency of telephone calls made to or from a target. A law enforcement agency is defined as a body that is authorised by law to carry out telecommunication interceptions, i.e. a particular communication involving a particular target.
To perform a lawful interception a law enforcement agency may monitor any one of a number of different identities that might be assigned to a target, for example the international mobile equipment identity (IMEI) of a target, international mobile subscriber identity (IMSI) and/or mobile station international ISDN number (MSISDN).
The IMEI, for example, is defined in the 3GPP standard TS 23.003. As can be seen from FIG. 1, the structure of the IMEI includes a Type Allocation Code (TAC) comprising 8 bits, a Serial Number (SNR) comprising 6 bits and a spare digit. A law enforcement agency may therefore, under lawful instruction, monitor a communication network for communication that is established through a particular user equipment device, i.e. using the serial number of that target device which is contained within the IMEI.
When a particular target device having a particular IMEI is earmarked as being suspect (for example because it is being used by a suspect person or organisation), then a lawful intercept may be ordered for that IMEI. The technical requirements for performing a lawful intercept are defined in 3GPP standards TS 42.033 and TS 43.033, plus the ETSI standard TS 101 671 relating to the handover interface for the lawful interception of telecommunications traffic.
A problem with performing this type of lawful interception on a particular target device is that the IMEI (or similar identity) of the target device must be known in the first place, so that the IMEI can be monitored prior to performing the lawful interception.